Non-prepublished German patent application No. DE 41 25 467 describes a sensor for simultaneously determining acceleration and differential pressure. The sensor has a membrane, for example, which separates two pressure spaces from one another and has a seismic mass suspended from it. The membrane is deflected either by compressive or accelerative forces. The deflection of the membrane is converted into an electric signal. If one of the two pressure spaces is sealed, it is possible for the absolute pressure prevailing in the other compression chamber to also be measured with such a sensor.
Because of its pressure-measuring function, such a sensor is suited, for example, for monitoring a tank venting installation, and because of its acceleration-measuring function, it is suited for detecting a rough road surface. In the above-mentioned German application, the sensor is expediently installed in a motor vehicle in a way that will allow severe up and down movements of the wheels to have an especially dynamic effect on its acceleration-measuring signal.
The above-mentioned German application indicates that the system for detecting rough road surfaces can be used to stop a misfiring recognition. German Patent Application No. DE 36 10 186 indicates that a signal for detecting rough road surfaces can be used to modify the performance characteristics of an anti-lock control system.
German Patent Application No. DE 41 25 467 does not indicate, however, how one is supposed to determine whether the pressure sensor having an acceleration-measuring function is more likely to output a signal that is decisive for the pressure within a certain time period, or whether it is more likely to output a signal that is decisive for the acceleration.